The invention relates to thermal management of processor-based systems.
Both hardware and software-controlled techniques exist for power and thermal management of processor-based systems. Software-based solutions are primarily utilized in connection with mobile platforms.
The software-controlled techniques involve an interrupt generated when a processor temperature setting is exceeded. The processor may be throttled after detecting an over temperature condition by polling processor temperature. Generally, the software-controlled solutions have a slower response time than the hardware-controlled solutions. In addition, there tends to be overshoot and undershoot problems with software-controlled solutions. The sensors utilized in software-controlled solutions are relatively slow and inaccurate. The on-die sensor (which is normally a diode) is not located on the hottest part of the processor die.
The hardware-controlled solution, used in systems other than mobile systems, involves a processor that automatically engages processor throttling, reducing the effective clock rate when a temperature condition is exceeded and disabling throttling when the processor is sufficiently cool. The hardware-controlled solution is based on an on-die binary sensor that indicates whether the processor is either hot or not hot. An interrupt capability may be available but is generally not utilized by the operating system due to the infrequency of throttling in desktop systems which are the primary applications for hardware-controlled solutions. As a result, operating systems may be unaware of hardware-controlled throttling.
The software-controlled solution is based on the premise that the platform exposes a variety of trip points to the operating system. A trip point is a temperature for a particular thermal region when some action should be taken. As the temperature goes above or below any trip point, the platform is responsible for notifying the operating system of this event and the operating system then takes an appropriate action.
When a temperature crosses a passive trip point, the operating system is responsible for implementing an algorithm to reduce the processor's temperature. It may do so by generating a periodic event at a variable frequency. The operating system then monitors the current temperature as well as the last temperature and applies an algorithm to make performance changes in order to keep the processor at the target temperature.
While current versions of hardware-controlled throttling reduce the frequency of the processor by rapidly stopping and starting the processor, future versions of hardware-controlled throttling may reduce the performance state of the processor by reducing both frequency and voltage. Because the hardware-controlled throttling is directly activated and has an extremely fast response time, the trip point for triggering the passive thermal management can be set near the high temperature specification of the processor (known as the junction temperature), thereby delivering high performance for most system designs.
Software-controlled throttling is exposed to the operating system, allowing the operating system to know the processor performance at all times. This becomes especially important with future operating systems that guarantee some quality of service based upon the processor performance to the executing applications. This concept is known as guaranteed bandwidth allocation and is based on the processor's current performance level.
Hardware-controlled throttling is advantageous in that it delivers the best possible performance in any given thermal solution, has extremely fast response time and does not throttle prematurely. A disadvantage to hardware-controlled throttling is that the operating system is completely unaware that the processor performance has been altered. Because of this, it may be expected that hardware-controlled throttling may cause issues with future operating systems that implement a guaranteed bandwidth scheduling.
Thus, there is a need for thermal management solutions that achieve advantages of both hardware and software-controlled techniques.